Nature and extent of the burden and risks associated with participation, benefit and group relatedness: at baseline a clinical examination, laboratory analysis, cardiopulmonary exercise testing, echocardiography and cardiac magnetic resonance imaging will be performed. All of these examinations will be repeated at 3-months follow-up except for the cardiac magnetic resonance imaging. All examinations, except for the MRI, are part of the standard workup in our hospital for patients undergoing implantation of a CRT device. Data needed for the purpose of this study, will be acquired by offline image analysis with dedicated software.